Tuning indicator for carriersignal receivers



R. T. HINTZ TUNING INDICATOR FOR CARRIER-SIGNAL RECEIVERS Filed March 27, 1940 INVENTOR ATTORNEY Patented Aug. 25, 1942 TUNING INDICATOR FOB. CARRIER- SIGNAL RECEIVERS Robert T. Hintz, Woodhaven, N.

Hazeltine Corporation,

Y., assignor to `a corporation ot Dela- Application March 27, 1940, Serial No. 326,149 8 Claims. v(Cl. Z50-40) The present invention relates to improved tuning indicators for carrier-signal receivers and, particularly, to tuning indicators of the cathode-ray tube type especially suitable for use in tunable frequency-modulated carrier-signal receivers.

Carrier-signal receivers conventionally -are provided with an adjustable tuning means for tuning the receiver toa desired carrier signal which may comprise either conventional adjustable tuning elements or preselector tuning elements which may be selectively connected into the receiver circuit and a vernier tuning element to procure more precise tuning. Inasmuch as inaccurate tuning of the receiver frequently results in undesirable distortion of the received signal, the cause of which may not be recognized by thelistener, it is further conventional to provide the receiver with a visual tuning indicator by which the receiver may be more precisely tuned to` a desired carrier signal. The tuning indicators of the prior art have been devised in large part for amplitude-modulation carrier-signal receivers and generallyv have consisted of some device for indicating theimagnitude of a unidirectional current or voltage derivedfrom, and varying with, the signal-carrier which, in turn, varies in accordance with the accuracy of tuning of the receiver to a signalcarrier wave of constant frequency. 'Ihe strength of the amplitude-modulated signals translated by the receiver, in general, is greatest when the receiver is accurately tuned to the de- Asired signal-carrier wave and the indication of over a broad frequency band. Thus, even though the intensity variations of received signals are not reduced by limiter devices until the signals have been extensively ampliiied in the receiver, it is diilcult with such broadly-tuned circuits to ascertain within a reasonable degree of accuracy the condition of tuning of the receiver to a received carrier signal where the tuning indicaenergy of the signal translated by the receiver,

tion is derived from the signal energy appearing in the signal channel of the receiver at some Point ahead of the limiter devices. While it is possible to provide a special signal-translating channel through which signal energy can be supplied to a tuning indicator or the prior art type, such special channel necessarily has relatively sharply-tuned circuits and it is dimcult to maintain these circuits properly ahgnecl with the tuned circuits oi' the receiver at the high carrier frequencies commonly used for frequency-modulation transmissions. 'I'his is especially true 'm regard to changesin the resonant frequency of the tuned circuits due to changes of humidity, temperature, and the like, and applies to' a marked extent to the maintenance of the same resonant frequency between the sharply-tuned circuits of the indicatory control channel and theA tuned circuits of the frequency-detector system normally employed in a frequency-modulation receiver. The tuning indicator arrangements oi' the prior art, therefore, are not suitable for use in frequency-modulated carrier-signal receivers.

It is an object of the invention, therefore. to provide a new and improved tuning indicator which, while of general application, is especially suitable for use in frequencymodulation receivers and one which avoids one or more of the above-mentioned disadvantages of the prior art devices,

It is a further object of the invention to provide a tuning indicator which visually indicates by the relative position, size, and symmetry of relative mean two luminescent areas produced on the screen of a cathode-ray tube the degree and direction of mistuning oi the receiver to `a received carrier signal.

In accordance with one embodiment of the invention, a tuning indicator for a carrier-signal receiver including an adjustable tuning means comprises a cathode-ray tube, an input circuit adapted to have applied thereto a unidirectional control potential, the magnitude and polarity of Whichvary in accordance with the degree and direction, respectively, of mistuning of the receiver on either side of the received signal. The tuning indicator also includes means for deriving from the unidirectional potential two unidirectional controlsignals varying in accordance therewith in opposite senses, and means responsive to the control signals for deflecting the` cathode ray of the tube to produce on the' screen of the cathode-ray tube two luminous areas, the positions of which on the screen' 2 visually indicate the degree and direction ci the mistimins.

For a better understanding of the present in vention, together with other and further objects thereof, reference is had to the following de= scription taken in connection with the eccome panying drawing, and its out in the appended claims.

Referring now to the drawing, Fig. lis a circuit diagram, partly schematic,7 or a complete carrier-signal receiver embodying the invention; Fig. 2 illustrates the deflection patterns produced under various tuning conditions oi the receiver upon the screen of the cathode-ray tuning indicator tube employed in the Fig. l embodi ment;'Fig. 3 is a circuit diagram of a modified form of the tuning indicator circuit of the invention; and Fig. 4 illustrates schematically a .modined cathode-ray tube construction which may be employed with any of' the forms, of tb" invention shown in the several ngures.

Referring now more particularly to Fig. 1, there is represented schematically a complete frequency-modulated carrier-signal receiver of a conventional design embodying the present invention in a preferred form. In general, the receiver includes a tunable radio-frequency amplier lI having its input circuit connected to an antenna system II, I2, and having its output circuit com nected to a tunablefrequency changer or oscil lator-modulator I3. Connected in cascade with the oscillator-modulator I3, in the order named, are an intermediate-frequency amplifier of one or more stages. anamplitude limiter I5, a frequency detector and tuning indicator system IS, more fully described hereinafter, an audio-frequency ampliner I1 of one or more stages, and a sound reproducer I8.

It will be understood that the various units just described may, with the exception of the frequency detector and tuning indicator i3, be of a conventional construction and operation, the details of which are well known in the art, renc dering further description thereof Considering lbriefly the operation of the receiver as a whole, and neglecting for the moment the operation of the frequency detector and tuning indicator I6 presently to be described, a desired frequency-modulated carrier signal is selected and amplied by the tunable radio-frequency amplifier I0, converted to a frequency-moduieted scope -will be pointed I mediate frequency of the receiver.- A condenser 2l is connected'between the high signal potential terminal or the primary tuned circuit 24, 23 and the mid-point of the secondary inductor 23. rl`he junction point of the resistors 22, 23 is connected to the mid-point of the secondary inductcr 26 to complete the direct current path for the rectified currents of the diodes 2n, 2I. An intermediate-frequency by-pa'ss condenser 3l is ccnnected across the resistors 22, 23.

The tuning indicator of the invention comprises a cathode-ray tube 32 of the type having a pair of defiecting electrodes 33 and 34, each adapted and arranged to deflect in diierent di- .36. In a conventional tube of this type, y anode has a truste-conical shape and the cathode is an elongated cylinder coaxially positioned with rections a beam of electrons emitted by a cathode 35 and attracted to a fluorescent screen or anode the respect to the anode. The defiecting electrodes are generally rods of i a diameter appreciably smaller than that of electrodes being positioned .with their axes parellel to each other and to the axis of thecathode ybut spaced. from the cathode on opposite sides thereof. The circuit of deiiecting electrode I3 is connested through a pair of tandem-connected direct current ampliners 31 and 4l and through an audio-frequency filter, comprising a shunt condenser 43 and a series resistor 41, to the highpotential terminal of the resistors 22 and 23 in series. The deflection electrode 34 is similarly connected through a single direct current amplifier l and through the audio-frequency lter Atti, it to the high-,potential terminal of the resistors 22 and 23 in series. Operating current tor the amplifiers and 4I is supplied through load. resistors 38 and 42, respectively, from a ,source of operating potential +B as indicated.

In considering the operation of the circuit just described, it win be, seen that the frequencyresponsive network I9 and frequency detector are, in general, similar to conventional frequency-discriminating networks utilized in automatic frequency control systems of the prior art and utilize the principle of rectifying separately the sum and diderence of the voltages across the primary and secondary of a double-tunedcircuit and combining differentially the rectified voltages so obtained to provide a unidirectional voltage the magnitude intermediate-frequency carrier signal in the esfcillator-modulator I3, amplified in the interina diate-frequenoy ampliiier I4, limited to a pre determined substantially constant ampiitude by the limiter I5, and detected by the frequency detector I6, thereby to derive the audio-fretniency modulation components.` The audio-frequency' components are, in turn, amplified in the audiofrequency amplifier i1 and are reproduced by the Y sound reproducer circuit including a condenser 24 and an inductor 23 inductively coupled to an inductor 25 of a secondary circuit tuned by a condenser 21. primary tuned circuit tuned circuit 26, 21 are The 24, 25 andf the secondary the degree and direction,

and polarity of which vary in accordance with respectively, of mistuning of the receiver on either side of a received carrier signal.

Assume. that the receiver is accurately tuned to a desired carrier signal so intermediate-frequency carrier signal has a mean carrier frequency equal to the mean resonant frequency of the intermediate-frequency selectors oi the receiver. Under these conditions, the unidirectional potentials produced across the resistors 22, 23 are oi equal magnitude but of opposite polarity.' The audio-frequency filter 43, #il removes the audio-frequency modulation components from this unidirectional potential and there is, therefore, nopotential supplied through the audio-frequency lter 46, 41 to the amplifiers 31, 4I.` The normal operatingv currents oi these amplifiers cause a normal potential drop to appear across the load resistors 33 and 42, respectively, thereby biasing. the deilecting electrodes 33 and 34 to their normal operating potentials. The particular types of vacuum tubes employed tuned to the mean inter- Z5 yin the Aamplifiers 40 and 4I and the particular the cathode, the denecting that the modulated diiierential potential mined by the action of 38 and 52 are so chosen that the normal operating potentials of the delecting electrodes arellecting electrodes 33 and 34 produces an individual shadow angle on the uorescent anode 3G, the size of which varies with the magnitude of the control signal applied to the respective electrodes. The resultant shadow angles produced by the deilection electrodes are, therefore,

equal. Each of the de- Y the equal luminous areas are represented by the light portions C and D.

Now assume that the receiver is mistuned to one side of a received carrier signal. The vmodulated intermediate-freguency carrier signal appearing at the output of the limiter I5 has a mean carrier frequency different from that of the mean resonant frequency ofthe intermediate-frequency selectors oi' the receiver. The frquency-responsive network I9 now operates to I supply a larger potential to one of the diodes 2U, 2l than to the appears across the resistors 22, 23. In this event, there the audio-frequency filter 46, 4-1 to the ampliiiers 3l, 4i a unidirectional potential the magnitude the degree of mis'- This potential is reversed in polarity in ampliers 3l and di and again reversed in polarity in amplier dil and the transconductances of the ampliers and the circuit constants are so proportioned that equal and opposite variations side of the received carrier signal. 'I'hese control signals are applied to trodes 33 and 3c of the cathode-ray tube 32 to produce equal and opposite variations of their operating potential.

The unsymmetncal deiiection pattern produced other and a unidirectionalv the deiiecting elecis supplied through load resistors 4on the screen of cathode-ray tube 32, under these conditions, is shown 'in Fig. 2b. There is thus provided by the several shadow angles and luminousareas independent direction of mistuning desired carrier signal. size of the illuminated cwrangles of the two deecting electrodes, vary' not only in mean position but also in size or relative areas.

From the foregoing, it is evident that mistunng of the receiver aired carrier signal to that previously assumed to the opposite Side ci. the devisual indications which indicate both the degree or magnitude and the cathode-ray tube the resistors the result that the control signals applied to the 34 have the sense ally indicates, by the relative positions and areas of the luminous areas C" and D", the degree to which the receiver is mistuned from the received carrier signal and that the receiver is mistuned in a direction opposite to that which produced of Fig. 2b, the shadow angle B being smaller than the shadow angle lItis therefore apparent that in the arrangement of Fig. 1 the deilecting electrodes 33 and 34 constitute a pair of deecting 32, which pairpattern is symmetrical or cordance with the equality or inequality, tively, of the two unidirectional control to the defiecting electrodes 33 respecsi resistor 41. From the high potential side of the adapted to have applied thereto a unidirectional potential, the magnitude and polarity of which vary in accordance with the degree and `direc-v electrodes 33, 34l are thus included for applying to the detiecting means 33 and u the control signals for delecting the cathode ray oi the tube to produce a deflection pattern,- the symmetry-of which visually indicates the condition of tuning of nal. The deiiection pattern produced on the screen of the cathode-rayl tube includes two lumithe relative areas and the nous areas in which indicate the degree and mean positions visually direction of mistuning.

A modied form of the invention is'shown in Fig. 3, wherein elements corresponding to like elements of Fig. 1- are indicated by like reference characters. In this modification, a single pentode vacuum tube 48 is employed to provide and phase inversion of the unsymmetrical inacv 23, this inputl circuit is the receiver to the received sigofthe tube 48, comprising a suppressor electrode means for deriving from said unidirectional po- 49 and a cathode 5t, are connected through the tential two unidirectional control signals varying audio-frequency filter 45, si across the resistors n in accordance therewith in opposite senses, and 22, 23; The anode 5i and the screen lic both means responsive to said control signals for deserve as output electrodes, each being connected 5 fleeting the cathode ray of said tube to produce to one o the delecting ,electrodes 33 and 3s of Lon the screen of said cathode-ray tube two lumithe cathode-ray tube 32. The output electrodes nous areas, the relativemean positions of which 5| and 52 are energizedthrough resistors 53 and on said screen `visually indicate the degree and n 54, respectively, from a source oi operating poe` direction of said mistuning. tentlal +B as indicated. The resistors 53 and 54 10 2. A tuning indicatorfor a carrier-signal rehave values such that equal potentials are supceiver including an adjustable tuning means plied to the deflecting electrodes 33, when the comprising, a cathode-ray tube, an input circuit receiver isnot receiving any carrier signal and adapted to have applied thereto a unidirectional the characteristicsof tube A8 are such that concontrol potential, the relative magnitude and trol signals of equal and opposite values are depolarity of which vary in accordance with the veloped across resistors 53 and 54 in response to degree and direction, respectively or mistuning a control potential appliedV toits suppressor of said receiver on either side oi said received grid. Such'amplifying and phase-reversing cirsignal, means for deriving from said unidireccuit is disclosed and claimed in United States tional potential two unidirectional control sig- Letters Patent No. 1,997,665, granted April 16, ynals varying in accordance therewith in opposite 1935, upon the application of Harold A. Wheeler. senses. and means responsive to said control sig- The operation ofthe arrangement of Fig. 3 is nais for deecting the cathode yray of said tube identical to that of Fig. l, the amplifying and f to produce on the screen oi said cathode-ray phase-reversing tube 48 performing the function tube two luminous areas, the relative areas of of the ampliders 31, 40, and 4| of Fig. 1. 25 which visually indicate kthe degree and direction While it has been stated that the defiecting of said mistuning. electrodes 33, 34 of the cathode-ray tube 32 are s 3. A tuning indicator lor a carrier-signal reusually positioned 180 degrees apart on oppositek ceiver including an adjustable tuning means comsides of the cathode 35, as indicated in Fig. 2, prising, a cathode-ray tube, an input circuit y it will 'be evident that the deflecting electrodes 3c adapted to have applied thereto a imidire'ctional may be spaced a lesser angle than 180 degrees, ycontrol potential, the relative magnitude and as illustrated in Fig. 4. If this is done, care polarity of which vary in accordance with the should be exercised in so positioning the deflectdegree and direction, respectively of mistuning ing electrodes with respect to the cathode and of said receiver on either side of said received' in so biasing these electrodes that the shadow 35 signal, means for deriving from said unidirecangles A and B permit only a narrow luminous o tional potential two unidirectional control sigline M to appear between them, as indicated in nals varying in accordance therewith in oppo- Fig. 4a, under the condition oi exact tuning of site senses, 'and means responsive to said control the receiver to a received carriersignal. The signals 'for deflecting the cathode ray `or said position of the line M for exact tuning oi the re- 40 tube to produce on the screen of said cathode-ray ceiver to a received carrier signal may be indi tube two luminous areas, the relative areas and cated by a fixed indicator 51. Detuning the remean positions of which visually indicate the deceiver on one side of thepreceived signal has the gree and direction of said mistuning.

eilect that a luminous line M', Fig. 4b, moves to 4. A tuning indicator for a, carrier-signal reone side of the indicator 51 to a degree depend- 45'ceiver including an adjustable tuning means ing upon the degree of mistunng o the receiver. comprising, a cathode-ray tube, an input circuit Similarly, mistuning the receiver to the opposite adapted to have applied thereto a unidirectional side of the received signal shifts the luminous potential, the magnitude and polarity o1.' which line M", Fig. 4c, to the opposite side o the indivary with the degree and direction, respectively cator 51, the extent of its movement varying in oi mistuning of said receiver on either side of said accordance with the degree of mistuning of the received signa, means for deriving from said receiver. If desired, the lower halt oi the cathunidirectional potential two unidirectional conode-ray tube screen may be mashed or denuded trol signals the relative magnitudes of whicl of fluorescent material to eliminate the luminous vary in accordance with the degree and direcareas N, N', and N", thereby leaving only the 5 tion of said mistuning, and means responsive t4 movement of the luminous line M to provide the said control signals for defiecting the cathod` visual tuning indication. ray of said tube to produce on the screen of sat While there have been described what are at cathode-ray tube two independent visual indi present considered to be the preferred embodcations which indicate the degree and directio ments of this invention, it will be obvious to those of said mistuning. skilled in the art that various changes and modi- 5. .n tuning indicator for a carrier-signal r4 cations may be made therein without departing ceiver including an adjustable tuning meal from the invention, and it is, therefore, aimed in comprising, a cathode-ray tube, input circu the appended claims to cover all such changes adapted to have applied thereto a unidirection and modifications as fall within the true spirit potential, the magnitude and polarity of 'whia and scope of the invention. vary in accordance with the degree and dire What is claimed is: tion, respectively, of the mistuning of said r l. A tuning indicator for a carrier-signal receiver on either side of said received sign ceiver including an adjustable tuning mans means for deriving from `said unidirectional t Comprising, a cathode-ray tube, an input circuit ,m teni-,iai two unidirectional control signals the r adapted to have applied thereto a unidirectional ative magnitudes of which vary in accorda! control potential, the magnitude and polarity with the degree and direction of said mistuni of which vary in accordance with the degree and and means responsive to said control signals direction, respectively, of. mistuning of said redefiecting the cathode ray ot said tube to p ceiver on either side oi said received signal, duce on the screen of said cathode-ray tubei luminous areas which visually indicate the degree and direction of said mistuning.

6. A tuning7 indicator for a carrier-signal receiver including an adjustable tuning means comprising, a cathode-ray tube, an input circuit adapted to have applied thereto a unidirectional potential, the magnitude and polarity of which vary in accordance with the degree and direction, respectively, of the mistuning of said receiver on either side of said received signal, means for utilizing said unidirectional potential to produce two unidirectional control signals the relative magnitudes of which vary with the magnitude of said unidirectional potential and the sense of the relative magnitudes of which varies with the polarity of said unidirectional potential, and means responsive to said control signals for deecting the cathode ray of said tube to produce on the screenof said cathode-ray tube two luminous areas which visually indicate the degree and direction oi said mistuning.

'1. A tuning indicator for a carrier-signal receiver including an adjustable tuning means comprising, a cathode-ray tube, a pair of deecting means for said cathode-ray tube adapted and arranged to produce a symmetrical or an unsymmetrical deflection pattern according to the relative magnitudes of control signals applied to said deecting means, an input circuit adapted to have applied thereto a unidirectional'potential, the magnitude and polarity of which vary in accordance with the degree and direction, re-

retent No. 2,29li,182.

ROBERT T. HINTZ vond coltunn, line 5l, claim and line t9, claim li,

requiring correcti on as follows:

strike out arelatlvei; line 55, Same'claim, after respectively Y e3 spectively, of the mistuning of said receiver on either side of said received signal, means for utilizing said unidirectional potential to produce two unidirectional control signals varying in accordance therewith in opposite senses, and means for applying to said deflecting means said control signals for deecting the cathode ray or said tube to produce a deflection pattern, the symmetry of which visually indicates the condition of tuning of said receiver to said received signal.

8. A tuning indicator for a carrier-signal receiver including an adjustable tuning means comprising, a cathode-ray tube, a pair of deiiecting means for said cathode-ray tube adapted and arranged to produce a symmetrical or an unsym metrical deection pattern according to the equality or inequalit respectively, of two unidirectional control signals applied to said deflecting means, an input circuit adapted to have applied thereto a unidirectional potential, the magnitude and polarity of which vary in accordance with the degree and direction, respectively, of

the mistuning of said receiver on either side oi"A said received signal, and means responsive to said unidirectional potential for deriving and applying to said deflecting means equal unidirectional control signals when said receiver accurately is tuned and unequal unidirectional control signals when said receiver is mistuned on either side of said received signal.

ROBERT T. my.

CERTIFICATE OF CORRECTION.

August 25, lelie.

Page l1., secinsert a comme.;

Henry Ven Arsdale, 'Acting Commissioner of' Patents.

CERTIFICATE oF CORRECTION. patent No. 2,2sh,182. August 25, 1942.

ROBERT T. HINTz.

f the above mnnbered patent requiring correction as follows: Page 1L, sec

ond column, line 5l, claim, strike out "relative", libe 55, Samel claim,

and line )49, claim 1;, after respectively insert a comm; and that the Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

